Conventionally, HSDPA (High Speed Downlink Packet Access) is available as a high-speed packet transmission scheme based on a W-CDMA (Wideband Code Division Multiple Access) scheme. The HSDPA adopts HARQ. The HARQ (Hybrid Automatic Repeat reQuest) is a scheme which combines retransmission control (ARQ: Automatic Repeat reQuest) and error correcting coding processing.
A HSDPA-compliant base station adopts a “HARQ function” shown in step S807 in a flow chart of transmission data processing in FIG. 1. Data to be transmitted is subjected to turbo coding at a coding rate of ⅓ and the HARQ function performs a rate change to adapt the data to the number of physical channel bits to be actually transmitted.
The hardware configuration of this HARQ function is as shown in a block diagram in FIG. 2 and a second rate matching section 904 determines which bits should be transmitted using systematic priority parameter s and rate matching parameter r.
That is, the second rate matching section 904 determines how to execute rate matching (adaptation to the actual number of physical channels) on various types of data such as Systematic (hereinafter referred to as “systematic”), Parity1, Parity2 (hereinafter referred to as “parity 1” and “parity 2”) included in coded transmission data which has been turbo coded before being transmitted.
For example, the second rate matching section 904 determines transmission priority of systematic data or transmission priority of parity 1, 2 or in what pattern the bits of parity 1, 2 should be punctured (or repeated) etc.
Changing systematic priority parameter s and rate matching parameter r in this way allows different transmission bit patterns to be transmitted at the times of initial transmission and retransmission and makes it easier to obtain a coding gain.
Furthermore, when an HSDPA-compliant base station uses 16QAM (Quadrature Amplitude Modulation) as its modulation scheme, it further adopts Constellation Rearrangement (rearrangement of phase arrangement).
In this case, as shown in 16QAM rearrangement processing in step S810 of FIG. 1, in 16QAM, bit reliability varies between signal points. For this reason, by changing constellation rearrangement parameter b upon retransmission and changing the signal constellation, bit reality is equalized for ease of Turbo decoding and coding gain is achieved.
The HSDPA-compliant base station gives an RV (Redundancy version) parameter to two HARQ parameters (systematic priority parameters, rate matching parameter r) and constellation rearrangement parameter b, changes a rate matching pattern and constellation rearrangement (applicable to 16QAM only) for every transmission count to determine transmission bits.
When the modulation scheme of the HSDPA-compliant base station is QPSK and 16QAM, examples of setting of RV parameter Xrv are shown in Table 1 and Table 2.
TABLE 1Xrv(value)sr010100211301412502613703
TABLE 2Xrv(value)srb01001000211130114101510261037110
Table 1 shows set values of QPSK RV parameter Xrv based on the 3GPP TS25.212 specification and Table 2 shows set values of 16QAM RV parameter Xrv based on the 3GPP TS25.212 specification.
In Table 1 and Table 2, when systematic priority parameter s=1, transmission of systematic data is given priority and when systematic priority parameter s=0, transmission of parity data 1, 2 is given priority.
Furthermore, as is conventionally described in the 3GPP TS25.101 (see 3GPP TS 25.101 V5.5.0 (2002-12); Technical Specification Group Radio Access Network: UE Radio Transmission and Reception (FDD) (Release 5)), transmission is carried out with an RV parameter defined for every transmission count as shown in Table 3 and Table 4.
TABLE 3Transmission countTransmissionCountXrvsr1010221135024613
TABLE 4Transmission countTransmissionCountXrvsrb16103221113100045102
However, as described in the conventional 3GPP TS25.101 (Non-Patent Document 1) and shown in Table 3 and Table 4, transmission is carried out with an RV parameter defined for every transmission count according to a modulation scheme, and therefore there has been a problem that transmission according to the coding rate of transmission data and with an RV parameter corresponding to an appropriate transmission count is not carried out.
That is, an RV parameter is uniquely set according to the modulation scheme and transmission count and data is retransmitted by selecting a determined transmission bit pattern, and therefore there is a problem that a variation occurs in reception quality of retransmission data and the HSDPA-compliant base station cannot reduce the retransmission count.